Crawl space encapsulation systems are designed to extend the envelope of your home from the home’s subfloor to the floor and foundation wall of the crawl space. The encapsulation makes it so the crawl space is no longer impacted by the weather, but controlled and regulated to maintain conditions comparable to the inside environment.
Everyone thinks of crawl spaces as being dirty, wet, and musty. This is because most vented crawl spaces in humid climates are, in fact, dirty, wet, and musty. For decades, it was thought that venting a crawl space would keep it dry by allowing airflow. Unfortunately, as many homeowners are already aware, venting crawl spaces does not keep them dry or clean. Engineers and home builders began looking for better ways to keep crawl spaces dry, as the entire structural integrity of the home begins with the crawl space. What has been found is that the best and sometimes only way to keep a crawl space dry and structurally sound is to encapsulate the space.
Building materials and designs have changed over the years; some of these changes have amplified the moisture issues in crawl spaces.
Homes built before 1950 were constructed of old-growth lumber. Old-growth lumber was milled from trees 100 to 150 years old and is structurally stronger and more rot-resistant than today’s lumber. Today’s building lumber is from new-growth lumber, generally milled from trees that are between 12 and 20 years old. Today’s lumber is more prone to holding moisture and therefore more likely to have wood rot or mold growth occur.
Central air conditioning systems are also relatively new in the home. Central air conditioning started popping up in homes in the 1950’s but as more of a status symbol than a commonplace convenience. It wasn’t until the mid 1970’s that central air conditioning started to become widely found in homes across America. Ductwork for these systems are primarily installed in the crawl space. Ductwork not only cuts off airflow in the crawl space, it also has a lower surface temperature due to the cold air flowing through it.
Condensation begins when the surface temperature of a material falls below the dew point. For a majority of the year in the southeast, the average dew point is higher than the surface temperature of ductwork. Vented crawl spaces in the southeast with ductwork in them will consistently have condensation issues on and around the ducts. The only way to prevent this is to encapsulate the crawl space, which lowers the dew point and prevents condensation.
The combination of the building industry using a softer, more absorbent wood for framing along with ductwork being installed in the crawl space has ushered in the need for crawl space encapsulations in many homes found in the southeast.
Advanced Energy, out of North Carolina, did a case study comparing vented crawl space and encapsulated crawl spaces. The results of those case studies can be reviewed at www.advancedenergy.org